The present invention relates generally to an access device for providing access between a lower level and an upper level. More particularly, the invention is concerned with an improved drive mechanism for moving the access device between an operative position and a stowed position.
Access devices of the general type to which the present invention relates are known. One such device is described in Australian Patent 672706. The device described provides for access between a lower level and an upper level by providing a pair of rigid arms on each side member of the access device, such that, the device is pivotally moveable from a stable lower position to a stable upper position.
It is desirable that in some circumstances that the drive mechanism be relatively compact and an object of the present invention is to provide an access device which can meet this requirement.
According, to the present invention there is provided an access device for providing access between a lower level and an upper level the access device including a main body mounted for pivotal movement about a main body fixed pivot mounting between an access position in which it enables access between the upper and lower levels and a stowed position in which a substantial part thereof is disposed above the main body fixed pivot mounting; a drive mechanism operable to cause movement of the main body between the operative and stowed positions, the drive mechanism including a drive device and a link mechanism, the drive device comprising a linear actuator which includes a body portion pivotally mounted to a fixed structure and a drive member which can move in the direction of its longitudinal axis in a linear fashion relative to the body portion, the link mechanism including control link means mounted for pivotal movement about a control link fixed pivot mounting, the control link means being operatively connected to the drive member at a fist connecting point, the main body fixed pivot mounting and the control link fixed pivot mounting being laterally disposed to the same side by the longitudinal axis of the drive member, coupling link means operatively connecting the main body to the control link means, the coupling link means being connected to the main body at a second connecting point, spaced from the main body fixed pivot mounting, the arrangement being such that actuation of the drive member causes linear movement thereof which causes the connection between the coupling means and the main body to be displaced upwardly or downwardly to move the main body between the access position and the stowed position.
Preferably the upwards/downwards displacement of the first connection point is substantially less than the upward/downward displacement of the second connection point during movement between the access and the stowed positions.
Preferably the connection between the control links means and the coupling link means is such to cause the coupling link means to move towards a generally upright orientation when the main body is moved towards the stowed position.
Preferably the first connection point is adapted to swing through a substantially flat arc with respect to the horizontal when moving between the two positions.
In one preferred form the drive device may include an hydraulic piston/cylinder assembly, the cylinder being pivotally mounted to a fixed structure and the piston being operatively connected to the control link means at the first connecting point.
Preferably when the main body is in the access position the first connecting point is disposed above the connecting point between the control and coupling links and when in the stowed position the first connecting point is disposed below the connecting point.
The main body may in one form include an elongated member which in the access position, extends between the upper and lower positions with one end thereof being adjacent or resting on the lower level and the other end being adjacent the upper level and in this position, the main body being inclined with respect to a vertical axis and in the stowed position is disposed generally upright above the upper level and preferably vertically above the main body pivot mounting point. For example the main body may be in the form of a ladder or stairway or a ramp.
Preferably, the control link pivot mounting and the first and second connecting points are spaced from one another so that a line drawn from the first connecting point to the control pivot mounting and then from the control link pivot mounting to the second connecting point is generally V-shaped.
Preferably, the linear actuator is disposed generally horizontally.
The device may further include a hand rail assembly which includes a frame section operatively connected to the main body by at least one support arm, the or each arm being pivotally mounted between the main body and a fixed support so that it can pivot during movement of the main body between the access and stowed positions thereby permitting displacement of the frame section and a guide arm operatively connected between the fixed support and the main body or support arm to regulate the displacement of the main body.